Method and equipment for transmitting terminal interface user data and status information

ABSTRACT

The invention relates to a mobile system in which the radio interface rate of a traffic channel and the intermediate rate of a transmission channel restrict the number of bits available for the transmission of terminal interface statuses (S), network independent clocking (N) and subchannel numbering (#) of a multichannel data link. In the invention, the bits form a subframe (n, . . . , n+10) and the status and control information are multiplexed inside successive subframes in a superframe structure (SUPERFRAME). In other words, the capacity of the bits available for the control information is shared by various kinds of control information by means of the superframe structure.

This application is the national phase of international applicationPCT/F197/00633 filed Oct. 17, 1997 which designated the U.S.

The invention relates generally to data transmission in atelecommunication system, and particularly to data transmission in whichthe maximum transmission capacity of a traffic channel is as high as oronly slightly higher than one user data rate at a terminal interface.

Mobile systems generally mean different telecommunication systems thatenable private wireless data transmission for subscribers moving withinthe system. A typical mobile system is a public land mobile networkPLMN. The PLMN comprises fixed radio stations (base stations) located inthe service area of a mobile network, the radio coverage areas (cells)of the base stations providing a uniform cellular network. A basestation provides a radio interface (air interface) in the cell forcommunication between a mobile station and the PLMN.

Another field of mobile systems includes satellite-based mobileservices. In a satellite system, radio coverage is obtained bysatellites instead of terrestrial base stations, the satellites being inorbit round the earth and transmitting radio signals between mobilestations (or user terminals UT) and land earth stations (LES).

Subscriber mobility requires similar solutions in satellite mobilesystems as in the PLMNs, i.e. subscriber data management, authenticationand location management of mobile subscribers, handover, etc. Thesatellite systems should also support similar services as the PLMNs.

One way of meeting the above requirements in satellite mobile systems isto use existing PLMN solutions. In principle this alternative is verystraightforward since a satellite system can basically be compared to abase station system of a mobile system having a different radiointerface. In other words, it is possible to use conventional PLMNinfrastructure where the base station system(s) is(are) a satellitesystem. In such a case, the same network infrastructure could, inprinciple, even contain both conventional PLMN base station systems andsatellite ‘base station systems’.

There are many practical problems, however, in adaptation of the PLMNinfrastructure and a satellite system. A problem apparent to theApplicant is that a PLMN traffic channel and a traffic channel of a‘radio interface’ in a satellite system differ considerably. Let usexamine an example where the PLMN is the Pan-European digital mobilesystem GSM (Global System for Mobile Communication), and the satellitemobile system is the Inmarsat-P system that is currently beingdeveloped.

At present, a GSM traffic channel supports data transmission at userrates 2400, 4800, 7200 and 9600 bit/s. In addition to user data, statusinformation on the terminal interface (control signals of a V.24connection) is transmitted in both directions on the traffic channel. Intransparent HSCSD data service, it is also necessary to transmitsynchronization information between subchannels. In synchronoustransparent bearer services, the clocking information of networkindependent clocking NIC must also be transmitted through a transmissionchannel from a transmitting terminal equipment to a receiving terminalequipment via a transmission network, when the transmission network andthe transmitting terminal equipment are not in sync with each other,i.e. the terminal equipment uses network independent clocking (e.g.internal clock). The above-mentioned additional information raises thebit rate at the radio interface to be higher than the actual user rate.The GSM radio interface rates corresponding to user rates 2400, 4800 and9600 bit/s are 3600, 6000 and 12000 bit/s. These signals are subjectedto different channel coding operations, which raise the final bit rateto about 22 kbit/s.

The Inmarsat-P satellite system requires that the standard data rates upto 4800 bit/s (e.g. 1200, 2400, 4800 bit/s) can be transmitted on onetraffic channel, and that the standard data rates exceeding 4800 bit/s(e.g. 9600, 14400, 19200 bit/s, etc.) can be transmitted by usingseveral parallel traffic channels, like in the HSCSD service of the GSMsystem.

In the Inmarsat-P satellite system, the data rate of one traffic channelat the radio interface is at most 4800 bit/s, which equals the user datarate of 4800 bit/s at the terminal interface. In a data serviceemploying two traffic channels, the data rate at the radio interfaceequals the user data rate of 9600 bit/s at the terminal interface. Aproblem arises when not only the user data but also the above-describedterminal interface status information and any inter-subchannelsynchronization information should be transmitted over the radiointerface. The protocol data unit, i.e. frame structure, used by thesatellite system at the radio interface should therefore be defined tocarry the above-mentioned control and synchronization information overthe radio interface.

One approach would be to use a GSM solution, i.e. a V.110-based framestructure, also at the radio interface of the satellite system. However,this would be a very complicated solution, and it would significantlyreduce the user data rates available. A single traffic channel could notsupport the user data rate of 4800 bit/s since a V.110 frame structureand the terminal interface status information raise the actual data rate(radio interface rate) to be higher than 4800 bit/s. Therefore thehighest standard user data rate on one traffic channel would be 2400bit/s. For the same reason, a two-traffic-channel data service could notsupport the user rate of 9600 bit/s, but the highest standard user datarate would be 4800 bit/s (or in some systems 7200 bit/s). Acorresponding decrease in the available data rates would also occur indata services employing more than two traffic channels. Such a solution,where the overhead information causes a significant loss of capacity,would not be satisfactory.

A similar problem can also arise when other types of radio interfaces,such as wireless telephone systems, are connected to the PLMNs.

A similar problem can also arise on other types of connections in whichthe radio interface rate is to be used as efficiently as possible. Forexample, a new 14400 bit/s traffic channel has been planned for the GSM.In order that the terminal interface statuses and any other controlinformation could be transmitted over the radio path in addition to the14400 bit/s user data, the radio interface rate, implemented on thepresent principles, must be higher than 14400 bit/s, about 18 kbit/s. Ahigher radio interface rate requires that the existing radio networksshould be re-designed and the intermediate rate (TRAU) raised so thatonly two subchannels could be put in one 64 kbit/s timeslot in the HSCSDservice (i.e. the efficiency decreases in a TRAU data link). Amodification of the TRAU frame might make it possible to decrease theintermediate rate to 16 kbit/s, whereby the efficiency of the TRAU datalink would not be impaired. The radio interface rate of 14400 kbit/s canbe formed, for example, from the present radio interface rate of 12000kbit/s by enhancing the puncturing that follows channel coding. Theradio interface rate of 14400 kbit/s could not, however, transmit thenecessary additional information with the user data rate of 14400kbit/s, but the actual user data rate would be below 14400 kbit/s. Theradio interface rate can be slightly raised (e.g. 100 to 300 bit/s) byenhancing the efficiency of the puncturing, and extra bits can beobtained thereby for the transmission of said control information. Theenhancement of the puncturing, however, impairs the ability of thechannel coding function to correct transmission errors.

In the above-described solutions, control information is transmitted ina frame structure (TRAU, radio burst) outside the user data stream.

Another approach, in which the control information is transmitted insidethe user data stream, is disclosed in the Applicant's parallel patentapplications FI 955,496, FI 955,497 and FI 963,455. These applicationsdescribe data transmission methods in which the terminal interfacestatus information and any other control or synchronization informationare transmitted through a traffic channel in the redundant data elementsof end-to-end protocols, such as the redundant parts of the protocoldata units of user data or the start and stop bit positions ofasynchronous data characters. The overhead information does thus notincrease the number of the bits to be transmitted, so the transmissioncapacity of the traffic channel (e.g. radio interface rate of 14400kbit/s) can be exactly the same as the user data rate at the terminalinterface (e.g. 14400 kbit/s). No additional puncturing is thus neededat the radio interface for the transmission of the control information.In high-rate data transmission (HSDSD) a data link comprises a group oftwo or more traffic channels, whereby the total capacity of the group oftraffic channels can be the same as the user data rate at the terminalinterface.

Both the above approaches, however, pose an additional problem.

When the status and control information are transmitted in redundantbits inside the user data stream in the redundant data elements of theend-to-end protocols, then the transmission is dependent on theredundancy of the end-to-end protocols. Not all end-to-end protocolscontain a sufficient number of redundant bits for carrying the terminalinterface status bits, subchannel numbering bits and NIC code bits. Thismeans that these protocols cannot be supported at all in transparentdata transmission.

When the status and control information are transmitted on a trafficchannel outside the user's end-to-end data stream, the transmission ofuser data is completely transparent, i.e. any end-to-end protocolwhatsoever can be used. A problem, however, is that for example in theGSM a TRAU frame is not able to carry the terminal interface statusbits, the subchannel numbering bits and the NIC code bits at theintermediate rate of 16 kbit/s. The intermediate rate of 16 kbit/srequires a frame structure that is so compact that there is no room forthis additional information. On the other hand, a higher intermediaterate would restrict the number of subchannels in HSCSD transmission, asstated above.

The object of the invention is to eliminate the above problems.

The invention relates to a data transmission method according to claim10, an equipment according to claim 8, and a mobile system according toclaim 15.

The bits available for the transmission of the extra controlinformation, such as the terminal interface status bits, the subchannelnumbering bits and the NIC code bits, form a subframe, and two or moresubframes form a superframe. In the invention, the information is thenmultiplexed inside successive subframes in the superframe structure. Inother words, the capacity of the bits (subframe bits) available for thetransmission of control information is shared in the time domain byvarious kinds of control information by means of the superframestructure. Preferably one, optionally several such bits in each subframeare used to form a superframe structure, i.e. to indicate at least wherethe superframe starts and optionally where it ends, and to produce thesynchronization information. The remaining subbit or subbits are used totransmit the various kinds of status and control information inmultiplexed form inside the superframe thus formed. The superframe bititself can also be used to transmit the status and control information,if the superframe locking character is shorter than the number of bitsreserved for it in the superframe.

The invention allows transmission of terminal interface status andcontrol information and other control information, subchannel and/orframe numbering of a multichannel connection, and NIC codes, even if thenumber of available bits in one transmission frame or end-to-end userdata protocol unit is smaller than the total bit number of theinformation to be transmitted. The only requirement is that in eachframe or each end-to-end user data protocol unit the number M of bitsavailable for this purpose is at least 2, if the superframe bit itselfis not to be used or cannot be used for transmission of status orcontrol information. If one and the same bit is used both forsuperframing and for the transmission of the status and controlinformation, M can be 1. The size of the superframe, i.e. the number Lof subframes within the superframe, depends on the total number N ofbits to be transmitted and the number M of available transmission bitsper subframe, being thus L≧M/N. Generally, N>M≧1 and L≧2.

The invention is equally well suited for the transmission of controlinformation both outside and inside the user data stream.

When data is transmitted in a frame structure (such as TRAU) outside theuser data stream, the invention eases the pressure put on theintermediate rate and thereby allows a larger number of subchannels inmultichannel data transmission (HSCSD). In addition, the number ofadditional bits needed at the radio interface (radio interface rate) canbe reduced, which in turn decreases the need of additional puncturing.

The invention makes transmission inside the user data stream possiblewith all end-to-end protocols in which there are at least two bitsavailable in the redundant data elements for the transmission of statusand control information.

The term ‘subframe’ is here to be understood in a very general sense. Inthe invention, a subframe comprises the bits reserved for thetransmission of the control information to be multiplexed inside anactual transmission frame or in the redundant data elements ofend-to-end protocols, such as the redundant parts of the protocol dataunits of user data or the start and stop bits of asynchronous datacharacters. A ‘superframe’ in turn is a unit comprising two or more suchsuccessive frames.

In the following the invention will be described by means of preferredembodiments with reference to the attached drawings, in which

FIG. 1 is a block diagram illustrating a configuration for datatransmission in accordance with the GSM recommendations,

FIG. 2 is a block diagram illustrating the transmission of 28800 bit/suser data, terminal interface status and control information, NIC codesand subchannel/frame numbering via two GSM traffic channels, each ofwhich has a radio interface rate that is higher than 14400 bit/s,

FIG. 3 shows a TRAU frame for an intermediate rate of 16000 bit/s and auser rate of 14400 bit/s,

FIGS. 4 and 5 show superframes according to the invention,

FIG. 6 shows a HDLC frame,

FIG. 7 shows a common asynchronous character sequence, and

FIGS. 8 and 9 illustrate formation of a protocol data unit transmittingstatus information.

The present invention can be applied to data transmission through anytraffic channel whatsoever, provided that the maximum data rate of thechannel is equal to or slightly higher than the user data rate at theterminal interface. The traffic channel can be implemented by anymultiple access technique, such as time division multiple access (TDMA)and code division multiple access (CDMA). The invention is obviouslyapplicable in the new 14400 bit/s channel type of the GSM, the 9600bit/s channel type of the CDMA, and the 4800 kbit/s channel type of theInmarsat-P satellite system.

The preferred embodiments of the invention will be described below withreference to a 14400 kbit/s traffic channel of a GSM-based mobilesystem. The invention, however, is not to be understood as being limitedto these systems.

The structure and the operation of the GSM mobile system, defined in theGSM specifications of the ETSI (European Telecommunications StandardsInstitute), are well known to those skilled in the art. Reference isalso made to GSM System for Mobile Communication by M. Mouly and M.Pautet, Palaiseau, France, 1992; ISBN:2-9507190-0-7. The GSM-basedmobile systems include the DCS1800 (Digital Communication System) andthe U.S. digital cellular system PCS (Personal Communication System).

FIG. 1 illustrates a configuration for data transmission according tothe GSM recommendations. FIG. 1 shows the basic structure of a GSMmobile system. The GSM structure comprises two parts: a base stationsystem BSS and a network subsystem NSS. The BSS and mobile stations MScommunicate via radio connections. In the base station system BSS, eachcell is served by a base station BTS (not shown). A number of basestations are connected to a base station controller BSC (not shown),which controls the radio frequencies and channels used by the BTS. TheBSSs are connected to a mobile services switching centre MSC. CertainMSCs are connected to other telecommunication networks, such as thepublic switched telephone network PSTN and the ISDN.

In the GSM system, a data link is established between a terminaladaptation function TAF of an MS and an interworking function IWF in themobile network (usually in the MSC). In data transmission taking placein the GSM network, this connection is a V.110 rate-adapted, UDI-codeddigital fullduplex connection that adapts to V.24 interfaces. The V.110connection described herein is a digital transmission channel originallydeveloped for ISDN (Integrated Services Digital Network) technology. Itadapts to a V.24 interface, and also allows transmission of V.24statuses (control signals). The CCITT recommendation for a V.110rate-adapted connection is presented in the CCITT Blue Book: V.110. TheCCITT recommendation for a V.24 interface is presented in the CCITT BlueBook: V.24. In non-transparent data services, a GSM connection alsoemploys a radio link protocol RLP. The TAF adapts a data terminal TEconnected to the MS to the above-mentioned GSM V.110 data link, which isestablished over a physical connection utilizing one or more trafficchannels (HSCSD). The IWF comprises a rate adapter that adapts the GSMV.110 data link to a V.24 interface, and a data modem or another rateadapter, depending on whether the connection is extended to the PSTN orthe ISDN. The ISDN protocols can be, for example, V.110 or V.120. In theISDN or the PSTN, the data link is established, for example, to anotherdata terminal TE. The V.24 interface between the MS and the TE is herecalled a terminal interface. A corresponding terminal interface is alsofound in the IWF, and for the other data terminal TE in the ISDN or thePSTN. The protocol used between the terminal equipments TE can be, forexample, a HDLC protocol described in ITU-T recommendation X.25 or, infacsimile transmission, a protocol according to ITU-T T.30.

In the GSM, data is typically transmitted in TRAU data frames betweenthe base station BTS and a specific transcoder unit TRCU(Transcoder/Rate Adaptor Unit) in the network. At present, the TRAU dataframe is a 320-bit frame (20 ms), whereby the intermediate rate is 16000bit/s at the present user data rates. The TRAU frame and its use aredefined in GSM recommendation 08.60.

A GSM traffic channel supports data transmission at user rates 2400,4800, 7200 and 9600 bites. In the future, high-speed data services(HSCSD=high speed circuit switched data) employing two or more trafficchannels at a radio interface (multi-slot access) will also supporthigher user rates (14400 bit/s, 19600 bit/s, . . . .) In addition touser data, terminal interface status information (V.24 interface controlsignals), such as CT105 (RTS=request to send), CT108 (DTR=data terminalready), CT106 (CTS=clear to send), CT107 (DSR=data set ready) and CT109(CD=data carrier detect), is also transmitted in V.110 frames in bothtransmission directions. Further, in multichannel transparent HSCSD dataservice it is also necessary to transmit inter-subchannelsynchronization information by which the order of data bits receivedfrom different subchannels can be restored. The above-mentionedadditional information increases the bit rate at the radio interface tobe higher than the actual user rate. The radio interface ratescorresponding to user rates 2400, 4800 and 9600 bit/s are 3600, 6000 and12000 bit/s.

The frame structure used for data transmission over a V.110 connectionis described in greater detail e.g. in the GSM recommendations, and inFinnish Patent Applications No. 955,496 and 955,497.

It should be noted that the status bits of the V.110 frame are only anexample of terminal interface status information and other informationthat would normally have to be transmitted in V.110 frames or otherframes through a traffic channel. It is not essential to the invention,however, what the status information or any other control orsynchronization information that is transmitted in addition to the userdata actually contains. The invention is generally applicable totransmission of all such overhead information. More generally, theinvention is applicable to transmission of all data that contains otherinformation as well as user data.

A conventional GSM traffic channel thus has additional capacity fortransmitting the necessary status and synchronization information, aswell as the user data. With reference to a 14400 bit/s traffic channel,we shall now study cases in which there is no additional capacity (radiointerface rate 14400 bit/s) or in which the capacity is to be maintainedsmall (radio interface rate>14400 bit/s).

As stated above, the interface rate of 14400 bit/s can be formed fromthe interface rate of 12000 bit/s by increasing puncturing. Thepuncturing deletes some of the channel-coded bits before transmission inaccordance with a predetermined rule.

In channel coding, for example a 72-bit information block can besupplied to a channel coder every 5 ms. Four such blocks areconcatenated in the coding process, and four tail bits are added. Theresult is a 292-bit block, coded with a ½-rate convolution code. Thecoding yields 584 coded bits. The coding is punctured so that 128 bits(every 5^(th) bit) are not transmitted. The result is a block of 456coded bits.

The capacity obtained from the channel coding can be used to raise theradio interface rate (data rate before and after channel coding) to14400 bit/s or even above that. A drawback is that the efficiency of thechannel coding is impaired, i.e. the bit error ratio increases and thecoverage area of the cellular network is thereby decreased.

Radio Interface Rate Above 14400 Bit/s

When the radio interface rate is above 14400 bit/s, the status andcontrol information of the terminal interface, the NIC codes and thesubchannel/frame numbering of the HSDSD can be transmitted in radiobursts and TRAU frames outside the user data stream. FIG. 2 illustratesthe transmission of 28800 bit/s user data, the terminal interface statusand control information, the NIC codes and the subchannel/framenumbering via two GSM traffic channels, each of which has a radiointerface rate that is higher than 14400 bit/s.

As stated above, it would here be advantageous that the intermediaterate, i.e. the TRAU frame transmission rate, would not exceed 16 kbit/s(between the BSS and the MSC/IWF). This requires a new kind of TRAUframe. FIG. 3 shows an optimized TRAU frame, which has been formed bydeleting all unnecessary elements from a conventional data framestructure and by reducing the frame to 640 bits (length 40 ms instead ofearlier 20 ms). The user data bits are placed in bit positions D1 toD576. The user data rate of 14400 bit/s can thus be transmitted at anintermediate rate of 16000 bit/s. In the new TRAU data frame, which istransmitted all the way between the base station BTS and the IWF (i.e.via or past the TRCU), control bits C6 to C9 (which in FIG. 3 areindicated by SP, SP, SP and D0) are not needed for the purpose currentlyallocated for them (some of the control bits are spare bits even in thepresent 320-bit TRAU frame). The bit positions can be used for thefollowing:

transmission of terminal interface statuses

transmission of channel/frame numbers of subchannels

transmission of NIC codes (transparent synchronous call)

control of discontinuous transmission DTX from an MSC to a BTS

separation of idle frames transmitted by the base station BTS from theframes of the synchronization step.

Since one bit is needed for the DTX control (bit position D0), themaximum of three bits C6 to C8 (SP) are available for the transmissionof other control information. This, however, is not sufficient, sincefor example the NIC codes typically require 5 bits, the terminalinterface status and control bits require 3 bits, and the HSCSDsubchannel and/or frame numbering requires 2 or 3 bits.

In the invention the problem is solved by multiplexing the differentkinds of control information inside the available bits in severalsuccessive TRAU frames. For this, the bits that are available for thetransmission of control information in a TRAU frame are used as asubframe, the subframes of two or more successive TRAU frames forming asuperframe, inside which said different kinds of control information aremultiplexed.

In a preferred embodiment of the invention the four ‘spare’ bits in theTRAU frame are used as follows:

1 bit: superframing

1 bit: status and control information (terminal interface statuses, NIC,subchannel frame numbering)

1 bit: DTX

1 bit: spare

the IWF can separate the idle frames of the BTS from the synchronizationframes of the traffic channel for example on the basis of the superframebit (an idle frame does not have a superframe structure, the bit isalways ‘1’), or the spare bit of the TRAU frame can be used for thispurpose.

FIG. 4 illustrates multiplexing according to the invention in theabove-described situation where there are two bits available in a TRAUframe for the transmission of status and control information, i.e. thelength of a subframe is two bits. From each subframe, one bit is usedfor the formation of a superframe and one for the transmission ofcontrol information. The total number of bits in the control informationto be transmitted is 11 bits, i.e.: three subchannel/frame numberingbits #, three terminal interface status bits S, and five NIC code bitsN. The superframe inside which the whole control information can bemultiplexed comprises 11 subframes. In the example of FIG. 4 thesubchannel/frame numbering bits # are transmitted in the first threesubframes (n . . . n+2), the status bits S of the terminal interface inthe next three subframes (n+3 . . . n+5), and the NIC codes N in thelast five subframes (n+6 . . . n+10). The start of the superframe isindicated by setting ‘0’ as the start bit in the first five subframes,and the end is indicated by setting ‘1’ in the last six subframes.

FIG. 5 illustrates a second example, in which all four bits are assumedto be available in a TRAU frame, i.e. the length of a subframe is fourbits. From each subframe is used one bit to form a superframe and threebits to transmit control information. The control informationtransmitted is the same as in FIG. 4, i.e. the total number of bits is11 bits. The superframe inside which the desired control information canbe multiplexed comprises 4 subframes, i.e. 12 bits. In the example ofFIG. 5 the subchannel/frame numbering bits # are transmitted in thefirst subframe (n), the status bits S of the terminal interface in thesecond subframe (n+1), and the NIC code bits N in the third and fourthsubframes (n+2 and n+3). In the extra bit position of the fourthsubframe is placed a fill bit F. The beginning of a superframe isindicated by setting ‘0’ as the start bit in the first two subframes,and the end is indicated by setting ‘1’ as the start bit in the last twosubframes.

The same principle can be applied to any number of status and controlinformation bits and to any number of bits available in a transmissionframe. Instead of the above-described bit patterns ‘11111000000’ and‘1100’, the frame structure can use any bit pattern whatsoever, forexample so that the effect of bit errors in superframe synchronizationcan be eliminated.

Also, additional puncturing and the subsequent decrease in the size ofthe coverage area of the cellular network are to be maintained as smallas possible. As a result, the number of additional bits needed at theradio interface should be minimized.

On account of this, in a preferred embodiment of the invention thechannel coding is punctured further (in addition to the puncturingrequired by the interface rate of 14400 bit/s) only by 1 bit/radio burst(duration of burst 5 ms), which means eight code bits/40 ms. When thecoding ratio is X/Y=1/2 (number X of bits before channel coding/number Yof bits after channel coding), four bits per TRAU frame (40 ms) areavailable for the transmission of terminal interface statuses and othercontrol information. In these bits it is possible to transmit said twobits of the TRAU frame on the connection MS-BTS. More particularly, thebits can be used, for example, as follows:

2 bits: detection of the halves of a double-length (40 ms) TRAU frame atthe reception (MS and BTS). This is not necessary with the earlier 20 msframe, since the beginning and the end are detected by means of radiopath synchronization. It must be possible to separate the halves fromeach other, so that in a non-transparent case the beginning of alengthened RLP frame can be detected, and in a transparent case thesuperframe structure, the data bits and the status and control bits canbe detected.

1 bit: superframing (like in FIG. 4)

1 bit: status and control bits (like in FIG. 4).

Let us now study end-to-end data transmission in the directionMS/TAF-MSC/IWF, with reference to FIG. 2.

The MS receives 28800 bit/s user data DATA and terminal interface statusand control bits STATUS from the terminal interface (data terminalequipment TE). In addition, the MS/TAF forms 5-bit code words of networkindependent clocking (NIC), as defined in GSM recommendation 04.21.Further, the MS/TAF generates the subchannel and/or frame numbering bitsof the HSCSD. In the example, multichannel data transmission uses twosubchannels for a user data rate of 28800 bit/s, the radio interfacerate of the channels being higher than 14400 bit/s and the intermediaterate being 16000 bit/s. Let there be four bits available on the radiopath and in the TRAU frames for the transmission of other than userdata. The MS/TAF multiplexes the terminal interface status and controlbits, the NIC code bits and the subchannel/frame number bits inside fourbits, as shown in FIG. 4, and sends them to the BSS.

Multiplexing based on a 40 ms TRAU frame sequence can be performed onthe radio path in different ways, and so the possibility of utilizingthe spare bits of the TRAU frame varies. For example:

1) The same 40 ms sequencing is used. On the connection MS-BTS one bitper 20 ms is used to separate the halves of a 40 ms sequence from eachother. Two bits remain for the superframing and multiplexing inaccordance with FIG. 4.

2) 20 ms sequencing of the radio path is used. The available 4 bits per40 ms are used so that two bits are used for superframing and two forthe transmission of status and control information. This can be used,for example, as a safeguard against bit errors, for example so that eachstatus bit is repeated or that both bits are used to transmit status andcontrol information without that bits are repeated, whereby even thespare bit of the TRAU frame can be used to transmit status and controldata.

3) 40 ms sequencing is used over the radio path. Only two bits insteadof four are introduced into use by additional puncturing. The timing ofthe ¤40 ms is conducted in the BTS and the MS on the basis of the framenumbering of the radio path. Said two bits conduct the superframing andthe multiplexing in accordance with the principle illustrated in FIG. 4.

If there are a sufficient number of bits available at the ratiointerface, for example 11, multiplexing is not needed. The BSS generatesTRAU frames, places user data bits in the frames and multiplexes thereceived control bits inside a superframe, as shown in FIG. 4. TheMSC/IWF receives the TRAU frames, separates user data from the framesand demultiplexes the NIC code bits, the subchannel numbering bits andthe terminal interface status and control bits from the superframe. The28800 bit/s user data and the terminal interface status and control bitsare supplied to the data modem of the IWF. The data modem communicatesin the common manner on a 28800 bit/s modem connection with another datamodem via the public switched telephone network PSTN, the latter modembeing connected to a receiving terminal equipment TE.

In the opposite direction of transmission, the MSC/IWF multiplexes theNIC code bits, HSCSD subchannel/frame numbering bits and the terminalinterface (data modem) status and control bits inside a TRAU frame, asshown in FIG. 4. The BSS separates the user data and said controlinformation from the TRAU frames and sends them further over the radiointerface to the MS/TAF. Like in the other direction of transmission,the control information can be in multiplexed or not multiplexed formwhen it is transmitted over the radio interface. Also in this directionof transmission it is possible to use either 20 ms or 40 ms sequencingover the radio path, as described above. The MS/TAF separates the userdata and the terminal interface status and control bits and suppliesthem to the terminal equipment TE.

Radio Interface Rate 14400 Bit/s

If the data rate and radio interface rate of the traffic channel at theradio interface are the same as the user data rate at the terminalinterface, for example 14400 or 4800 bit/s, there is no extra capacityon the traffic channel that could be used for transmitting otherinformation in addition to the 14400 or 4800 bit/s data. The terminalinterface status information and other control information are thentransmitted through a traffic channel in the redundant data elements ofend-to-end protocols, for example the redundant parts of the protocoldata units of user data or in the start and stop bit positions ofasynchronous data characters. For example, in the TRAU frame of FIG. 3the terminal interface statuses and other control information aretransmitted transparently within the data stream in data fields D1 toD576, and the control bit positions of the TRAU frame are not used forthis purpose.

Finnish Patent Applications 955,496 and 955,497 by the same Applicant,incorporated herein by reference, teach a synchronous and, respectively,an asynchronous data transmission method in which the above-describedprinciple can be utilized and the present invention applied.

In Finnish Patent Application 955,496, terminal interface statusinformation and any other control or synchronization information aretransmitted through a traffic channel in the redundant parts of theprotocol data units of the current transmission protocol(s). At thereceiving end the status information and any other information areseparated from the protocol data units, and the original redundancy isrestored to the protocol data units. The basis of this synchronoustransmission is that the frame structures of many transmission protocolscomprise redundant bits when they are used in the PLMN environment, e.g.in the GSM network, or as a result of repetition occurring in them, orfor some other such reason.

For example, the bearer services of the PLMN networks use apoint-to-point connection, i.e. a circuit-switched connection is usedbetween two points. Most transmission protocols are also meant forpoint-to-multipoint connections, in which case their frame structurecomprises an address field. The address field is redundant on apoint-to-point connection. The terminal interface status information andany other control or synchronization information are transmitted in suchan address field. The protocols include, for example, HDLC-based (highlevel data link) protocols.

A synchronous facsimile protocol according to GSM recommendation 03.45uses a HDLC frame according to FIG. 6 comprising a redundant ADDRESSfield at a binary-coded signalling stage and at an error-correctedfacsimile data transmission stage. It also comprises other stages inwhich GSM specific frames are sent. These frames contain redundancy inthe form of repetition of the same information.

If the facsimile service uses a normal facsimile data mode NFD accordingto ITU-T T.30, the data contains end-of-line chains (EOL),facsimile-coded data, and optionally stuffing data to make up theminimum line length. The stuffing can be considered redundant in respectof the transmission. Other protocols are described in greater detail inFinnish Patent Application 955,496.

The number of redundant bits available for the transmission of extracontrol information may be insufficient, in the same way as in the caseof 16 kbit/s TRAU frames. For example, the address of a HDLC frameprovides at most 8 bits (in practice 6 bits), whereas the NIC code bits,the HSCSD subchannel/frame numbering and the terminal interface statusbits can require 11 bits. The control information multiplexing accordingto the present invention can then be applied to the redundant bits offor example two successive HDLC frames.

In Finnish Patent Application 955,497, transmission of terminalinterface status information and any other control or synchronizationinformation is based on synchronous/asynchronous conversion, which isneeded at the transmitting end; when asynchronous characters aretransmitted through a synchronous traffic channel,asynchronous/synchronous conversion is needed at the transmitting end.The conversion defines rate adaptation, underrate processing, andoverrate processing. Underrate processing means that extra stop bitsSTOP are added between the asynchronous characters before transmission.Overrate processing means that STOP bits are removed now and then frombetween the asynchronous characters before transmission. This kind ofconversion is defined e.g. in ITU-T recommendation V.14, which also setsthe limits on the underrate and overrate.

The conversion can be used for transmitting the overhead information ofthe terminal interface by concatenating asynchronous characters to formlonger ‘protocol units’ and by removing the START bits and STOP bitsfrom between the concatenated characters, as shown in FIGS. 7, 8 and 9.The capacity made available by the removal of the start and stop bits isused for the transmission of status information. Standard underrate andoverrate processing and rate adaptation are applied to this new protocoldata unit PDU. The protocol data units are transmitted over asynchronous traffic channel to a receiver. The receiver synchronizeswith the START bits and performs operations that are reverse to thoseperformed by the transmitter. In other words, the receiver separatesfrom the protocol data unit asynchronous data characters, terminalinterface status information, and any other control or synchronizationinformation.

Even in this case the number of available bits may be insufficient,whereby the control information can be multiplexed inside the availablebits of two or more successive protocol data units in accordance withthe same principles that were described above in connection with theTRAU frames.

Both in synchronous and in asynchronous transmission, the multiplexingand demultiplexing according to the invention are conducted in theMS/TAF and the MSC/IWF. In the demultiplexing, the redundancy of theuser data protocol is restored. The control information passes betweenthe MS/TAF and the MSC/IWF inside the user data stream, and it is notprocessed separately.

The figures and the accompanying description are only intended toillustrate the present invention. The invention can vary in its detailswithin the scope and spirit of the attached claims.

What is claimed is:
 1. A method of transmitting terminal interface userdata and status information and any other control or synchronizationinformation in protocol data units through a traffic channel or a groupof traffic channels in a telecommunication system, comprising allocatingfor said status and control information a number of bits inside oroutside the user data bit stream from protocol data units, the number ofthe allocated bits being smaller than the total number of bits in thestatus and control information, using at least one of said allocatedbits to indicate a start of a superframe that includes said allocatedbits from at least two protocol data units from, and multiplexing saidstatus and control information inside said allocated bits within saidsubframe.
 2. A method according to claim 1, comprising allocating saidbits from redundant data elements of end-to-end protocols of theterminal interface, when said status and control information aretransmitted inside the user data bit stream.
 3. A method according toclaim 1, comprising subjecting a channel-coded signal to additionalpuncturing so as to raise a radio interface rate of the traffic channelto be higher than the highest user data rate of the traffic channel, andallocating said bits from a radio burst from among the additional bitsthat are produced by said additional puncturing.
 4. A method accordingto claim 1 or 3, comprising allocating said bits from a transmissionframe in which the user data is transmitted over the transmission linksof a mobile communication network.
 5. A method according to claim 4,comprising the transmission frame being a 640-bit Transcoder/RateAdaptor Unit data frame that is arranged to produce an intermediate rateof 16000 bit/s at a user data rate of 14400 bit/s, and by allocatingsaid bits from among the seventh and eighth bits of the second octet andthe first and second bits of the third octet of said 640-bitTranscoder/Rate Adaptor Unit data frame.
 6. A method of transmittingterminal interface user data and status information and any othercontrol or synchronization information in protocol data units through atraffic channel or a group of traffic channels in a telecommunicationsystem, comprising allocating for said status and control information anumber of bits from a transmission frame in which the user data istransmitted over the transmission links of a mobile communicationnetwork, the number of the allocated bits being smaller than the totalnumber of bits in the status and control information, using at least oneof said allocated bits to indicate a start of a superframe that includessaid allocated bits from at least L transmission frames, where L is aninteger and L≧2, multiplexing N-bit status and control information intosaid allocated bits inside said superframe that comprises L M-bitsubframes, where M and N are integers and N>M≧2, transmitting saidsuperframe in M allocated bits in L successive transmission frames overa transmission link of the mobile network, and transmitting saidsuperframe in M allocated bits in L successive radio bursts over theradio path.
 7. A method of transmitting terminal interface user data andstatus information and any other control or synchronization informationin protocol data units through a traffic channel or a group of trafficchannels in a mobile system including a high-rate data transmissionservice based on parallel use of two or more traffic channels assubchannels in one and the same data call, comprising allocating forsaid status and control information a number of bits inside or outsidethe user data bit stream from protocol data units, the number of theallocated bits being smaller than the total number of bits in the statusand control information, using at least one of said allocated bits toindicate a start of a superframe that includes said allocated bits fromat least two protocol data units, and multiplexing said status andcontrol information inside said allocated bits within said super-frame,said status and control information comprising terminal interface statusinformation, the subchannel and/or frame numbering of the high-rate datatransmission service, and the code words of network independentclocking.
 8. Transmission and reception equipment for transmitting theterminal interface user data and status information and any othercontrol information in protocol data units through a traffic channel ina telecommunication system, comprising a transmission equipment beingconfigured to multiplex N-bit status and control information inside asuperframe that comprises L M-bit subframes, where M, N and L areintegers and N>M≧1 and L>2, and the transmission equipment beingconfigured to transmit said superframe in M bits allocated from insideor outside the user data bit stream in L successive protocol data unitsover a traffic channel.
 9. Equipment according to claim 8, thetelecommunication system being a mobile communication system in which achannel-coded signal is subjected to additional puncturing so as toraise a radio interface rate of the traffic channel to be higher thanthe highest user data rate of the traffic channel, and the transmissionequipment being configured to transmit said superframe in M allocatedbits in L successive radio bursts over the radio path.
 10. Equipmentaccording to claim 8 or 9, wherein the user data is transmitted over atransmission link of a mobile network in transmission frames, andwherein the transmission equipment is arranged to transmit saidsuperframe in M allocated bits in L successive transmission frames overthe transmission link.
 11. Equipment according to claim 10, comprisingthe transmission frame being a 640-bit Transcoder/Rate Adaptor Unit dataframe that is arranged to produce an intermediate rate of 16000 bit/s ata user data rate of 14400 bit/s.
 12. Equipment according to claim 8,comprising the transmission equipment being arranged to transmit saidsuperframe in M redundant data elements of the end-to-end protocols ofthe terminal interface, when said status and control information aretransmitted inside the user data bit stream.
 13. Equipment according toclaim 8, comprising the equipment being a terminal adaptation functionof a mobile station, an interworking function of a mobile network, abase station or a land earth station of a satellite system. 14.Transmission and reception equipment for transmitting the terminalinterface user data and status information and any other controlinformation in protocol data units through a traffic channel in a mobilesystem including a high-rate data transmission service that is based onparallel use of two or more traffic channels as subchannels in one andthe same data call, comprising the transmission equipment beingconfigured to multiplex N-bit status and control information inside asuperframe that comprises L M-bit subframes, where M, N and L areintegers and N>M≧1 and L>2, and the transmission equipment beingconfigured to transmit said superframe in M bits allocated from insideor outside the user data bit stream in L successive protocol data unitsover a traffic channel, said status and control information comprisingterminal interface status information, the subchannel and/or framenumbering of the high-rate data transmission service and the code wordsof network independent clocking.
 15. A mobile communication systemcomprising transmission and reception equipment for transmitting theterminal interface user data and status information and any othercontrol information in protocol data units through a traffic channel,comprising means for multiplexing N-bit status and control informationinside a superframe that comprises L M-bit subframes, where M, N and Lare integers and N>M≧1 and L≦2, means for transmitting the superframe inM bits allocated from inside or outside the user data bit stream in Lsuccessive protocol data units over the traffic channel.
 16. A mobilecommunication system according to claim 15, comprising subjecting achannel-coded signal to additional puncturing so as to raise the radiointerface rate of the traffic channel to be higher than the highest userdata rate of the traffic channel, and the mobile station and the basestation being arranged to transmit said superframe in M allocated bitsin L successive radio bursts over the radio path.
 17. A mobilecommunication system according to claim 15, comprising the mobilestation and the interworking function of the mobile network beingarranged to transmit said superframe in M redundant data elements ofend-to-end protocols of the terminal interface inside the user data bitstream.
 18. A mobile communication system comprising transmission andreception equipment for transmitting the terminal interface user dataand status information and any other control information in protocoldata units through a traffic channel, comprising a multiplexermultiplexing N-bit status and control information inside a superframethat comprises L M-bit subframes, where M, N and L are integers andN>M≧1 and L≦2, a transmitter transmitting, the superframe in M bitsallocated from inside or outside the user data bit stream in Lsuccessive protocol data units over the traffic channel the base stationand the interworking function of the mobile network being configured totransmit said superframe in M allocated bits in L successivetransmission frames over a transmission link between the interworkingfunction and the base station.
 19. A mobile communication systemaccording to claim 18, comprising the traffic channel being a 14400bit/s traffic channel and the transmission frame being a 640-bitTranscoder/Rate Adaptor Unit data frame with a length of 40 ms, whichcorresponds to an intermediate rate of 16000 bit/s, and by theTranscoder/Rate Adaptor Unit data frame comprising 576 data bits for14400 bit/s user data and at most four bits for the terminal interfacestatuses, network independent clocking and subchannel or frame numberingof a multichannel data link.